Control device for prosthetic hands



April 24, 1951 M. J FLETCHER con'mor. DEVICE FOR PROSTHETIC HANDS Filed Ma f 20, 194';

6 Sheets-Sheet 2 war/c812 faker QH u April 24, 1951 M. J. FLETCHER CONTROL DEVICE FOR PROSTHETIC HANDS a Sheets-Sheet 3 Filed May 20, 1947 N m NW @N H SN y" WNN EM MQN wM \N% h \NN gm \N QWN r a e m j 6 Sheet s-Sheet 4 .0 U NWN M. J. FLETCHER CONTROL DEVICE FOR PROSTHETIC HANDS A ril 24, 1951 Filed May 20, 1947 wmw www www Zaur/ce 7. Wefcher 25 i 2 Aprii 24, 195i M. J. FLETCHER CONTROL DEVICE FOR PROSTHETIC HANDS Filed May 20, 1947 I r 6 Sheets-Sheet 5 IU H I HE HIWW 5i nuami'oc T M m H J April 24, 1951 M. J. FLETCHER 2,549,792

CONTROL DEVICE FOR PROSTHETIC HANDS Filed May 20, 1947 6 Sheets-Sheet 6 bk W 9 @N whw @N al'l'ornmr Patented Apr. 24, 1951 2,549,792 CONTROL DEVICE FOR PROSTHETIC HANDS Maurice J. Fletcher, Maxwell, Iowa, assignor to the United States of America as represented by the Secretary of War Application May 20, 1947, Serial No. 749,370

2 Claims. (Cl. 3-12) Granted under the act of March 3, 1883, as

amended April 30, 1928; 370 0. G. 757) The invention described herein may be manuiactured and used by or for the Government for governmental purposes, without payment to me of any royalty thereon.

time it will change automatically to a compounded leverage, whereby a greatly increased grip is obtained at the fingertips without additional load being placed on the operating mecha- The present invention relates to actuating in- 5 nism. strumentalities for prosthetic appliances, such as a A further object of the present invention is to resilient articulated fingers of an artif cial hand, provide a force amplifier of the above-indicated for example-or for spring-actuated fingers for entype, which is of extremely simple and rugged abling improved operation of the said fingers and construction and which requires no flexible cables, to impart sufficient strength to the fingers to en- Ohains puIIeys, sheaves, or gears, and their atable ready picking up of objects grasped by the tendant limitations. hand l A still further object of the invention i to pro- One of the principal impediments t th devide a force amplifier of the above-indicated type velopment of a satisfactory artificial hand has that can be utilized between any type of powerbeen the lack of strength of the hand at the closing and y type of s ce of a tuat g p w fingertips. This commonly is called fingertip such as muscle motion, shoulder shrugs, electric pressure. Due to the difiiculty of mechanically motive power or hydraulic or pneumatic operating operating a finger through a relatively slender means. column, a great mechanical disadvantage is in- A t ll further object of this invention is to proherent within a finger and t of t excursion vide a force amplifier of great strength and of exand power for operation of the mechanical hand r y l ght Weight, and one which can be reis taken up in attempting to close the hand against placed as a complete assembly. a tremendous mechanical disadvantage resulting A Still h r bj of e invention is o p i very l fingertip pressure, vide a force amplifier for artificial hands orthe It has been the desire of prosthetic researchers like Which permits extreme fioXibility as to e to provide a fast-closing action of the hand until Point Of mounting, Whether that point of o nta predetermined pressure or load is impressed at s e ve-elbow, below-elbow or in the hand the fingertips. At this time, it is desired that an itSe1fr automatic transmission be provided which will r her objects of the invention will become apcompound the leverage exerted at the fingertips Parent as e description p cee s, a d he feawithout a great deal of exertion and excursion betures of novelty Will be pointed o in particularity ing wasted over the entire range of closure of the in the pp d cl ims; and the invention confingers, sists in the construction, combination, and ar- Many difiiculties have been experienced in atrengement of the Various parts of the d v e o tempting to realize this objective. Most attempts a the objects mplated are attained as will that have been made involve the use of gears and be more fully set forth and hereinafter p e o t cables, but the use of gears has carried with it in the claims, a ll t n e acc mp nyin the burden of complication of mechanism and indrawingsa tolerable weight and has necessitated the use of It y be po d out before Proceeding. with flexible cables for the operation of the device. the present invention that e basic principle of In view of the stresses involved, these cables the force amplifier f the p s t invention is t be so large as t impair their flexibihtsrand that of automatic force transmission in which a consequently the cables are a source of continual force s app d o ne arm of a lever, and a reannoyance and maintenance. Furthermore, the Sistohoe is app o e oth r lever arm. When movement of all other force amplifiers known and the entire h n sm h s moved until the retried out prior to the present development has s n e has creased to a predetermined load, a been restricted as additional leverage could not slide bar in the force amplifier locks, and the be applied against av resilient object. balance of the force load then is compounded The present invention has for one of its printhrough the leverage andimpressed upon the recipal objects the provisions of an improved force sistant factor. If the resistant end of the mechamplifier for prosthetic appliance such as artianism is locked by a ratchet or the like to prevent ficial hands, which force amplifier can be imposed its returning, a return of the force portion of the between an artificial hand and an operating device to its normal position and reapplication of mechanism, for permitting a fast fanning action the force will cause the device to act recurrently of the fingers until a load is encountered, at which for obtaining a tighter grip or impressing further into the resistance factor. This jacking action is referred to hereinafter in the specification as multiple excursion. This action will be clarified in the following specification when taken in conjunction with the appended drawings, wherein Fig. l is a side elevation of one form of force amplifying mechanism constructed in accordance with the present invention, for use in operating articulated fingers of an artificial hand;

Fig. 2 is an end elevation of the mechanism of Fig. 1, looking from the left as viewed in Fig. 1;

Fig. 3 is a bottom view of the apparatus of Fig. 1;

Fig. 4 is a side elevation of a base unit employed in the construction of the mechanism of Fig. 1;

Fig. 5 is a side elevation of an assembly of the base unit of Fig. 4 and a sliding carriage plate mounted upon and guided by the base unit;

Fig. 6 is an end view of the assembly of Fig.5;

Fig. 7 is a bottom view of the assembly of Fig. 5;

Fig. 8 is a side elevation of one of the lever members employed in the construction of Fig. 1;

Fig. 9 is a side elevation of another of the lever members;

Fig. 10 is a side elevation of the lever member of Fig. 8, looking from the left as viewed in Fig. 8;

Fig. 11 is a bottom View of the lever member shown in Fig. 8;

Fig. 12 is a side elevation of a somewhatmodified form of construction of the force amplifier of the present invention, the view showing the mechanism in open position;

Fig. 13 is a sectional elevation along the line XIIIXIII of Fig. 12, looking in direction of the arrows;

Fig. 14 is a sectional plan view along the line XIVXIV of Fig. 12, looking in the direction of the arrows;

Fig. 15 is a front elevation of one of the lever members shown in Fig. 12;

Fig. 16 is a side elevation of the lever shown in Fig. 15;

Fig. 1'? is a view similar to Fig. 12 but showing the mechanism in closed position;

Fig. 18 is an end View of the mechanism as viewed from the left in Fig. 1'7

Fig. 19 is a bottom view of the assembly of Fig. 1'7;

Fig. 20 is a front elevation of a base plate employed in the modification of Fig. 12;

Fig. 21 is an end view of this plate, looking from the left as viewed in Fig, 20;

Fig. 22 is a front plan view of an assembly of base plate and slidable carriage plate, similar to the showing of Fig. 5, but illustrating the modified structure embraced in Fig. 12; I

Fig. 23 is an end view of the assembly as viewed from the left in Fig. 22;

Fig. 24 is a front elevation of a slide member operating in the base plate of Fig. 20, to which slide the carriage plate of Fig. 22 is attached;

Fig. 25 is an end View of the slide of Fig. 24, viewed from the left in Fig. 24;

Fig. 27 is a side elevation of the embodiment of the construction shown in Fig. 1, the construction being shown in open, or expanded, position;

Fig. 28 is a View indicating one manner of connecting the device of the present invention to an artificial hand.

Referring more particularly to the drawings, it will be observed that except for details of shape of the levers and the manner of connecting the lever together, the two modifications illustrated Fig. 26 is a bottom view of the assembly of Fig.

in the drawings are substantially identical in construction and operation. Hence, the same reference characters will be applied to like parts in both modified embodiments of the invention, except that the similar reference characters are primed in Figs. 12 through 26. Thus, reference character A represents a base portion or plate, and B i a movable carriage member or plate mounted on the base plate A and slidable relative thereto, as will be described in greater detail hereinafter.

The base plate A is provided with a T-slot running in the direction of movement of the device, this T-slot 30 accommodating a slide 32 that is secured to the carriage member B by screws 34.. The base plate A has milled, on one of the marginal edges, a series of ratchet stops or teeth 36, as shown clearly in Fig. 4, for example, for a purpose which will be described hereafter. Base plate A is provided with a plurality of holes 38 as shown in the drawing for reducing the weight thereof, it being understood that the device of the invention is to be made as lightas is consistent with strength, for maximum comfort to a user of a prosthetic hand. The slidable carriage unit B also may be provided with holes for weight reduction and for the reception of screw studs, as will be pointed out hereinafter. The slidable carriage unit B isprovided with a dependent resttricted portion 49, a hol 42 being present adjacent to the end of this restricted portion for the reception of a pivot stud 44 for a bell-crank lever 46. Also suitably located on the carriage unit B adjacent to the periphery thereof is a hole 48 for reception of a pivot stud 59 for a second bellcrank lever 52.

The bell-crank levers 48 and 52 are convenie'ntly identical in size and shape, they having a short arm 54 and a long arm 56. Short arms 54 of lever 52 is pivotally connected at 58 to the outwardly extending shackle 60 having a threaded chuck portion 62 on which is threaded the adjustable turnbuckle 64 in which a rather stiff finger-operating cable or link 66 is secured.

The long arm 56 of the lever 46 is pivotally connected at 68 to shackle 70, which is identical with shackle 6G and has a threaded chuck por tion H on which is received turnbuckle 12 in which a relatively stiff cable or link 14 is received and suitably locked. Cable 14 passes to a muscle motor or other source of energy, not shown, which may be of various types as will be mentioned hereinafter. Shackles S0 and 10 extend in opposite directions as shown. The long arm 56 of lever 52 and short arm 54 of the lever 46 are interconnected by a split link bar 16. As is indicated by Fig. 1, for example, short arm 54 of the levers is approximately half the length of the long arm 56 of the said levers, but this is not critical.

It will be noted also from the drawings that a ratchet pawl T! is rotatably mounted on a stud 78 that passes through the slidable carriage plate B. This pawl is adapted to engage the teeth of the ratchet 36 at predetermined intervals or when predetermined force conditions are applied to the force-amplifying construction of the present invention. Also, a coil spring 82 is provided which is maintained in predetermined and preset tension between the stud which forms the pivot point for lever 52 and the stud 34 which forms a pivot point for lever 46. This arrangement places the spring close to the pivot point of lever 46, so that the spring tension does not increase appreciably at any point in the movement between the levers 52 and 46; and these levers are so positioned that when a given force causes them to separate, the pawl TI is forced into engagement with ratchet teeth 36. It will be observed that the connecting link I6 also is mounted on stud 84 and also on stud 86 in the end of long arm 56 of lever 52. Levers 46 and 52 obviously are provided with suitable holes 81 and 90 for the reception of such studs, and also with holes 92 for the fulcrum studs.

It will benoted that the pawl is carried by an enlarged head 94 of stud I8, the-stud I8 being mounted on carriage plate B. This enlarged head 94 also carries an actuating pawl 96, which is longer than pawl 11, and which extends into the cut-out recess 98 in the carriage plate B. A spring I is coiled around the stud head 94, one end of the spring being held under nut I02 of fulcrum stud 44, the other end of which spring is secured to the pawl 96. Lever arm 56 carries a pin I04, which is adapted to engage the pawl 95 when tension on the cable I4 is released.

When the cable I4 is pulled, the pull is transmitted to lever arm 56, the arm 56 being pulled towards the right as viewed in Fig. 1, the parts assuming the position shown in Fig. 27 when fully open. This movement pulls the pin I04 away from engagement with the pawl 96, and also pulling the carriage plate B towards the .right as viewed in Fig. 1, until the limit of movement of the levers is reached. The resulting movement of the levers stretches spring 82 and as the pin I04 pulls away from engagment with the pawl 06, the tension or the spring I00 turns the stud 18 until the pawl I! is brought into engagement with the ratchet teeth 36. During this operation pivot 68 is pulled with an amplified force, the amount of which is dependent upon the eifectiv-e lengths of 'the bell-cranks and the amount of movement permitted to the arms thereof. The amplified force transmitted through cable 66 to the hand I06, acts to'close the fingers of the hand with sufficient strength to enable a desired object to be picked up by the wearer of the hand. u e

' The engagement of pawl IT with ratchet teeth 36 enables the use of the appliances to ease up somewhat on the pull exerted on cable 14, until the eased pull on the cable balances the pull of spring 82 without there being any change in the position of the parts, because of the locking engagement of the pawl with the ratchet teeth. However, when the pull of the spring 02 becomes eifective, the pin I04 comes into pressing engagement with pawl 05 depressing the pawl 96 and also bringing pawl 1'! out of engagement with the teeth I6 of the ratchet. The fingers of the handmay open because of their resiliency re-.

sponsively to release of the cable 66, pulling'the carriage member back to its original position. The provision of the rack and pawl structure permits a certain amount of relaxation on the part of the wear without releasing the grip of the fingers of the hand.

The second embodiment of the present invention is shown in Figs. 12 through 25, which embodiment differs from the precedingly-described form principally in the shape of the levers that produce the force amplification.

In Figs. 12 through 25, A represents a base plate, and B represents a movable carriage member or plate mounted on the base plateA and slidable relative thereto, as described previously above. The base plate A and carriage plate B are assembled and operatedrelative to each other as described above, the carriage plate 13' being slidable relatively to the base plate when the fingers of the hand encounter a load.

In order to effect the relative movement between the carriage plate B and the base plate A the latter is provided with a T-slot 30' accommodating a slide 32' that is secured-to the carriage B by screws 34. Also, as described above, the base plate A. is provided along the underside of the guide for the, slide bar with a series of rack slots or teeth 36', asshown clearly in Fig. for example, for a purpose similar to the rack teeth 36. 1

The input lever of this modification, see Fig. 12, for example, is a substantially straight lever member 94 that is fulcrumed on stud 96 which mounts lever 94 to the carriage plate B. Stud 96 is secured to the plate B adjacent toa corer of lower end 98 of the plate B, which lower end is off-set from the remainder of the plate and terminated in a substantial point I00, in the area of which point is mounted and secured a stud I02, for the purpose to be pointed out hereinafter.

The link 94' has an outwardly projecting lug I04 near the upper end thereof in which is mounted an inwardly projecting pin I06, the head portion of which is substantially larger than the shank portion I08 which is secured in the lug I04. At a suitable distance from the upper end of the link 94 and extending oppositely from the pin I06, there is mounted a second pin I I0, having an annular groove I I2 therein for receiving an end of coil spring II4, the other end of which spring is secured-to the lug I02, so that the spring II4'is maintained under a predetermined and pre-set tension between the pin H0 and lug I02.

At the upper end of link 94 there is secured the input assembly cable II6, this being the force inputcable, the input assembly being similar in. construction to that of the previously: described modification. The pivotal connection of;the force input asembly is indicated at N8, the assembly comprisingturnbuckle II9, shackle I2I and threaded chuck I23. Connected to the lower end of the lever 94' is a link I20, the connection being apivot pin I22, which connects one end of the link I20-to the lower end of the lever 94. Link I20 is pivotally connected at I23 to the lower end of le'ver I26, which has a curved portion I28 adapted to form a clearance for lower end I00 of the carriage plate B. Y

The lever I26 is fulcrumed on pivot stud I30, which connects the lever I26 to the carriage plate B. The upper end of the lever is pivotally connected at I32 to the output assembly including connection shackle I34, chuck I36 and turnbuckle I38, by means of which the cable I40 is adjusted as to tension. Stud I42 mounted in the carriage plate B carries the pawls I44 and I46, pawl I44 being adapted to engage the rack teeth 36 when the device of the invention is in expanded position, and to be released therefrom when tension on the input cable "I I6 is released sufficiently to enable the spring II4 to release the carriage plate B until pin'I 08 carried by the lever 94' engages the pawl I40, and turns this pawl, together with the stud I42 until thepawl I44 disengages the rack teeth 36, and the lever 04 and plate B are brought by spring II4 into fully retracted position as shown inFig. 17.

In the lever arrangements shown in the two modifications, the power output is substantially the same, the. ratio of power output to power 7 input being substantially four to one in both forms.

The construction of the present invention permits a fanning action of the fingers I48 pivot'ed to the hand I50, as indicated at '12, until a load encompassed by the fingers is met, at which time the carriage plate B, B is held in position of its movement relative to the base A, A at the first separation of the levers, and the leverage is com-pounded to gain strength at the output side at the expense of distance at the input. Upon release of the input power, the resiliency of the fingers opens them and returns the carriage plate to starting position. A spring 1 I54, connected as shown, resiliently maintains the fingers normally in open position.

'Where the hand 1 50 is provided with a finger lock mechanism 56 to prevent return movement of the fingers until desired which finger lock mechanism is provided in the output side of the improved device of the invention, a relaxation of the input motive power will cause the levers to return to position and take up the slack thus presented at the output end of the devices so that the carriage plate 13, 13' moves towards the input side -a suificient distance to permit the pawl l-7, M4) to gain several notches, or teeth of the rack, at which time an additional movement of the motive source will actuate the levers again, thereby causing a jacking action to give additional movement at the finger tips under power.

The practical operation of the device (either modification) is as follows:

The spring (82 or H4) is pre-set for a given load or pressure at the fingertips. For example, suppose that it is desired that the fingers move freely until they encounter a load resistance of five pounds. Thus, where a five-pound load is encountered by the fingers, which are attached to the output side of the device, the spring will yield, causing therpalwl :(T! or 'l' 'i l) to engage the rack teeth (36 or 36) thereby preventing "further movement toward the output side of the device, and the levers will compound to provide a force amplification. Both racks are silent in their operation. In both modifications, two levers are shown. These .two levers have the advantage of continuing the direction "of null. One lever can be used, but due u) restriction of space within an -artificial hand, such an arrangement generally is inconvenient. There may be employed four, six, or any number of ilevers, the levers being linked together to obtain the "leverage ratio "desired 'between the input and output sides of the device,

and these levers may be "straight, as shown in the foregoing-described second modification of the construction, or they maybe bent at their fulcrums to iorrn bell-crank levers, as shown in the first modification to -facilitatearrangement of the force amplifying device at any advantageous point in a prothesis. When the fingers are being opened :or closed under no lload, no action takes place 'b'etweenthe levers and the "whole carriage assembly :slides freely on the -base, r'giving, ineifeet, a single cable, :rod, for connection between the input'and the output.

The device an the present invention is rigid, simple in constru'ctionand does not require maintenance. It has been Ifound that the'complete de- 8 device can be used as an elbow lift or can be used on mechanical devices of various types requiring a smooth-acting automatic force amplifier. The spring (82, H4) can be made so that its tension is adjustable and the guide track may be double or single to obtain the proper center of thrust, and the proper rigidity required for a specific use.

Th force amplifier of the present invention can be used in conjunction with any type of force-clcsing mechanical hand, and can utilize any type of motive power, such as a shoulder sling, or hydraulic, pneumatic, or electric power, or with a muscle motor.

A sliding ype o'fxclutch (not shown) actuated by the levers in the same manner as the pawl presents an infinite number of locking points of the slidable carriage plate relative to the base plate, and gives greater efficiency to the jacking action which is generally called the multiple excursion characteristic of the device.

From the foregoing it will be apparent that the device of the present invention is capable of rather extensive modifications in structural details without departing from the spirit and scope of the invention and accordingly it will be understood that it is intended and designed to embrace within the scope of the invention such modification and changes as may be necessary to adapt it to varying conditions and use as defined by the appended claims.

Having thus described my invention, what I claim as new and wish to secure by Letters Patent is:

l. A control device for prosthetic hands, comprising a base member, a carriage member slid ably mounted on the base member for slidable movement relative thereto, power-input means adapted to be connected to a source of power, power-output means connected to a prosthetic hand foroperating the fingers thereof, a plurality of levers pivotally mounted on the carriage member, one of the levers being connected to the power-input means and thereby being the powerinput lever, another of the said levers being connected to the power-output means and thereby being the power-output lever, the pivotal mountings of the levers constituting the fulcrum therefore, the power-input lever having a short arm between the power-input means and the fulcrum, and a long arm between the fulcrum and the other end of the lever, the power-output lever having a long arm extending between the powerinput means and the fulcrum, a link interconnecting the long arm of the input lever to the short arm of the output lever, a spring attached to at least one of the levers and maintained under a pre-set tension, whereby upon application of power to the power-input means to operate the fingers of the hand, the carriage member with the levers mounted thereon, together with the power input means .and the power output means, moves as a unit along the base member towards the source "of input power without separation of the levers until the fingers engage a load, whereupon further application of power to the input means causes the levers to separate at the limit of movementof the carriage member, thereby producing a predetermined multiplication of power to the fingers thereby enabling the fingers to grasp and pick up the load, locking means efiective at the end of the movement of the carriage member against return, and means carried by one of the levers .for releasing the locking means -responsively "to return of the levers to closed position under action .of the spring respon- 9 sively to relaxation of input power, thereby permitting return of the carriage member responsively to the opening of the fingers to its original position.

2. A prosthetic appliance comprising, in combination, a prosthetic hand, a power-multiplying mechanism arranged to operate the fingers of the hand to flex the fingers forwardly towards the hand to close the fingers responsively to application of a predetermined input power to the said mechanism and to cause the fingers to grasp an object responsively to an increase in the input power, the said mechanism including a plurality of compounded levers adapted to predeterminedly multiply the input power and to convert the input power into predeterminedly multiplied output power to the said fingers, a carriage member for the levers and a base member for the carriage member, instrumentalities pivotally mounting the levers on the carriage members while permitting the levers to move relatively to the levermounting carriage, a rack on the base member, a pawl on the carriage adapted to engage the rack and to interlock therewith responsively to the carriage reaching its limit of movement towards the source of input power for preventing return of the carriage member responsively to the relaxation of the input power while permitting return of the levers to original position relative to the lever-mounting carriage, the said pawl being rotatably mounted on the carriage, an actuating pawl operatively associated with the lock ing pawl for releasing the locking pawl from engagement with the rack res'ponsively to the levers assuming their original position, means carried by one of the levers for engaging and operating the actuating pawl for moving the locking pawl away from the locking position with the rack, and means in the said fingers operative responsively to relaxation of input power to the power-multiplying mechanism for opening the fingers and pulling the lever-mounting carriage and levers to original position relative to the base and hand.

MAURICE J. FLETCHER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,230,378 Eberle Feb. 4, 1941 FOREIGN PATENTS Number Country Date 111,073 Great Britain Nov. 15, 1917 315,024 Germany Sept. 22, 1919 828,272 France Feb. '7, 1938 

